Modern endodontic treatment involves removal of the damaged pulp, followed by cleaning and shaping of the root canal space, irrigating, and filling with biocompatible material such as gutta-percha and a root canal sealer.
Shaping of the canal is performed either manually, using a series of stainless steel hand-held files, or mechanically, using rotary nickel-titanium files adapted to fit a standard or dedicated dental handpiece.
The manual process relies on the experience of the dentist, is physically difficult to perform and is time-consuming. The use of files requires repeated changing between numerous different rat-tail files, progressively increasing from the smallest to the largest. Its reach to the apical constriction for educate widening and removal of the smear layer is limited. The reason for such limitations relates to the moderate elasticity of the steel files and the risk of fracture when excessive force is applied.
Although the field of elastic rotary nickel-titanium endodontic files has developed greatly over the last few years, fracture (separation) of nickel-titanium rotary files is still often reported, and hence the use of such is restricted. In order to overcome the fracture problem, a large range of dedicated handpiece systems, powered by slow speed transaction equipped with torque and speed control limitation circuits, have been developed, requiring a high level of professional skill for their operation. As a result, the cost of files and the related equipment per endodontic treatment became significantly higher and are typically operated only by experts in the endodontic field, while ordinary dentists use standard handpiece in a risky procedure.
Additionally the round cross-section of the file prevents adequate cleaning when the canal cross-section is oval or narrow in shape. In such cases, enlargement of the canal cross-section to accept the round cross-section of the file, may weaken or perforate the wall or the apical portion of the canal. The same risk of perforation applies in case of a curved root canal, where the file tends to follow the path of least resistance, acting rigorously on the convex walls within the reach of the file, and insufficiently over the concave portions.
US20070099149 entitled “Endodontic device and method of utilizing and manufacturing same” corresponding to IL 171705 in the name of the present applicant discloses an endodontic device for cleaning, filing or reaming root canals. The device includes one or more metallic, flexible strands having an edge, a working section, a connecting section and a coupling head connected thereto. The strands are coated along the working section with a thin layer of a binder having abrasive particles embedded therein. The flexible, longitudinal strands are so constructed that their outer surfaces serve as active filing surfaces.
In operation the strand section of the endodontic file is inserted into the root canal to the apex, and the strand or strands are mechanically rotated by a handpiece to a high speed. The thin, flexible portion of the device is centrifugally thrown against the canal wall following the natural curvature and complex cross-section of the root canal in exact manner. The whole contents of US20070099149 are incorporated herein by reference.
WO2008/102352 entitled “Endodontic file” corresponding to IL 181439 in the name of the present applicant and likewise incorporated herein by reference, it is further suggested to use an endodontic file comprising at least one cord and a wire wound around at least a major portion of the cord, the wire having an abrasive outer surface.
However, in both the above-mentioned references, the file is firmly gripped and forcibly rotated by a standard or dedicated high speed handpiece, normally having no means or even technical ability, while in such high rotation speed, to control the delivered torque due to the high inertia of the motor itself. As a result although intended for high speed operation, the file may break if for some reason sticking or locking of the cord in the root canal occurs during operation.
Consequently, there exists a need for limiting the transmitted torque in order to prevent breakage of the wire endodontic file in case of sticking. Such an additional safety measure in operation will encourage use of a high-speed rotary endodontic file by those dentists who currently refrain from using such devices for fear of damaging the dentine layer or perforating the root canal.